The security/tokens endpoint in 11.4 does not return the sharedKey as the documentation says it is supposed to. I was able to test an 11.3 portal and 11.3 does return the sharedKey.
In 11.4 the response to security/tokens?f=json is:
{"resources":["update"]}
Docs: https://developers.arcgis.com/rest/enterprise-administration/portal/tokens/
Is this a known issue?